Outboard motor

ABSTRACT

An outboard motor configured so that an engine is covered by an engine cover, an intake opening is provided to both sides of the engine cover, and air drawn into the engine cover from the intake opening is introduced to a throttle body. A discharging/interference-type muffler is provided partway along an intake channel for guiding air from the intake opening to the throttle body. The discharging/interference-type muffler is provided vertically in the interior of the engine cover, and the interior of the discharging/interference-type muffler is divided in two in the vertical direction.

TECHNICAL FIELD

The present invention relates to an outboard motor having an enginedisposed inside an engine cover and a throttle body for introducing airdrawn inside the engine cover through intake openings formed in theengine cover.

BACKGROUND ART

Outboard motors are known as disclosed in, for example, Patent Document1 below, which includes an intake duct provided on an engine cover thatcovers an upper part of an engine, the intake duct having an inletopening into an air intake chamber and an outlet opening into an airintake pipe. The air intake chamber communicates with the exterior ofthe engine cover through an air intake port in the engine cover. The airintake pipe communicates with a throttle body (throttle valve).

According to the outboard motor disclosed in Patent Document 1, air isdrawn into the air intake chamber through the air intake port in theengine cover, whereupon the air that has been drawn into the air intakechamber can be drawn into the air intake duct through the inlet. The airthat has been drawn into the air intake duct is then drawn through theoutlet of the air intake duct and into the air intake pipe, and the airthat has been drawn into the air intake pipe is then drawn into thethrottle body.

PRIOR ART LITERATURE Patent Document

[Patent Document 1] Japanese Patent No. 3608637

SUMMARY OF INVENTION Technical Problem

According to the outboard motor disclosed in the disclosure of PatentLiterature 1, the air intake port of the engine cover is disposed facingtowards a lateral side of the outboard motor when attached to the hull.Consequently, when air intake noise is produced together with air intakepulsations and shock waves while the engine is being driven, the airintake noise produced thereby is transmitted through the air intakeduct, in a lateral direction from the intake port of the engine cover.Thus, because the air intake noise is transmitted in a lateraldirection, it is not readily transmitted to the hull side. However, itis difficult to achieve sufficient reduction of air intake noise throughmethods involving transmission of air intake noise in a lateraldirection.

It is an object of the present invention to provide an outboard motorwhich is capable of reducing air intake noise to a sufficient extent.

Solution to Problem

According to a first aspect of the present invention, there is providedan outboard motor comprising: an engine; an engine cover covering theengine; intake openings provided in both lateral sides of the enginecover; and a throttle body for introducing air drawn inside the enginecover through the intake openings, characterized in that aninterference-type muffler for reducing air intake noise is disposedpartway along an intake passage configured to guide air from the intakeopenings to the throttle body, wherein the interference-type muffler isdisposed vertically inside the engine cover, and the interference-typemuffler has an interior bisected in a vertical direction.

In the invention according to a second aspect, preferably, theinterference-type muffler with the interior thereof bisected in thevertical direction comprises a pair of interference-type mufflersections including a first interference-type muffler section and asecond interference-type muffler section, wherein the intake passageincludes a dual system having a first intake passage section for guidingthe air from one of the intake openings provided in both lateral sidesof the engine cover to the throttle body, and a second intake passagesection for guiding the air from the other of the intake openingsprovided in both lateral sides of the engine cover to the throttle body,and wherein the first interference-type muffler section is disposedpartway along the first intake passage section, and the secondinterference-type muffler section is disposed partway along the secondintake passage section.

In the invention according to a third aspect, preferably, theinterference-type muffler has a drain port formed in a bottom thereoffor allowing water infiltrated inside the interference-type muffler tobe drained out.

In the invention according to a fourth aspect, preferably, the intakepassage is provided with a silencer for reducing air intake noise, thesilencer being disposed downstream of the interference-type muffler andupstream of the throttle body.

In the invention according to a fifth aspect, preferably, the outboardmotor of claim 1, further comprising: a tubular air intake guide sectiondisposed partway along the intake passage and capable of guiding in avertical direction air that has been drawn in from the intake openings;a vertical duct disposed downstream of the air intake guide section neara rear wall of the engine cover in such a manner as to be bisected in avertical direction for guiding laterally the air that has been guidedvertically by the air intake guide section; and vertical separation ribsfor impeding a flow of air that has been guided laterally by thevertical duct.

In the invention according to a sixth aspect, preferably, the duct hasan interior bisected in the vertical direction and comprises a pair ofduct sections including a first duct section and a second duct section,the intake passage includes a dual system having a first intake passagesection for guiding the air from one of the intake openings provided inboth lateral sides of the engine cover to the throttle body via thefirst duct section, and a second intake passage section for guiding theair from the other of the intake openings provided in both lateral sidesof the engine cover to the throttle body via the second duct section,and one of the separation ribs is disposed on the engine cover in aregion thereof opposing the first duct section, and another of theseparation ribs is disposed on the engine cover in a region thereofopposing the second duct section.

In the invention according to a seventh aspect, preferably, the duct hasa drain port disposed in a bottom section thereof.

In the invention according to an eighth aspect, preferably, the duct hasguide ribs disposed such that air directed into the duct is guidedtowards the separation ribs.

In the invention according to a ninth aspect, preferably, a silencerhaving a silencer chamber is disposed upstream of the throttle body inthe intake passage; the silencer including: a body section forming alower half section of the silencer chamber, the body section beingdisposed on a belt cover arranged covering from above a drive belt fordriving auxiliary machinery of the engine; and a cover section formingan upper half section of the silencer chamber, the cover section beingdisposed on the engine cover and being detachably disposed on the bodysection.

In the invention according to a tenth aspect, preferably, the silencerincludes a sealing material between the body section and the coversection.

In the invention according to an eleventh aspect, preferably, the intakepassage includes: a tubular air intake guide section disposed facing avertical direction in a region in which air drawn in through the intakeopenings flows in a substantially horizontal direction, the tubular airintake guide section being capable of separating water from air drawn inthrough the intake openings; a guide bottom section formed between theintake openings and the air intake guide section, and having a slopingshape of downward pitch towards the intake openings from the air intakeguide section; and a drain groove disposed in the guide bottom section,and adapted for guiding water separated by the air intake guide sectionfrom the air intake guide section towards the intake openings; the waterguided into the inlet openings by the drain groove draining out from theengine cover through the inlet openings.

In the invention according to a twelfth aspect, preferably, the draingroove is formed to have a downward pitch towards the intake openingsfrom the intake guide section.

In the invention according to a thirteenth aspect, preferably, the draingroove has an outer groove wall disposed closer towards the intakeopenings, and an inner groove wall disposed further away from the intakeopenings, a height of the outer groove wall being greater than a heightof the inner groove wall.

Advantageous Effects of Invention

In the invention according to the first aspect, intake openings areprovided in both lateral sides of the engine cover, and aninterference-type muffler is disposed partway along the air intakepassage extending from the intake openings to the throttle body.Disposing the interference-type muffler on the air intake passage allowsthe frequency band of air intake noise, which is a component producingparticularly high acoustic pressure in exhaust noise, to be attenuatedby the interference-type muffler. In so doing, when air intake noise isproduced along with air intake pulsations and shock waves while theengine is being driven, the air intake noise can be sufficiently reducedby the interference-type muffler.

In an ordinary outboard motor, dead space is present between the sidewalls of the engine cover and the engine. According to the presentinvention, the interference-type muffler is disposed in a verticalarrangement. Therefore, this dead space can be utilized to dispose theinterference-type muffler therein. This obviates the need to ensureadditional space for the interference-type muffler, and accordingly theoutboard motor can be made smaller (more compact).

In the invention according to the second aspect, the intake passage isprovided with a dual system having a first intake passage section and asecond intake passage section. Furthermore, a first interference-typemuffler section is disposed in the first intake passage section, and asecond interference-type muffler section is disposed in the secondintake passage section. Air intake noise in the first intake passagesection can be reduced by the first interference-type muffler section,while air intake noise in the second intake passage section can bereduced by the second interference-type muffler section. Air intakenoise produced during driving of the engine can thus be sufficientlyreduced.

In the invention according to the third aspect, a drain port is disposedin the bottom section of the interference-type muffler. Thisinterference-type muffler is disposed in a vertical arrangement.Consequently, water that has been drawn in together with air through theintake openings can be allowed to drip downward in the interference-typemuffler, whereupon the water dripping down to the bottom section candrain out from the interference-type muffler through the drain port. Thewater that has been drawn in from the intake openings can thus beseparated from the air in the interference-type muffler, so that onlyair is guided into the throttle body.

Specifically, the interference-type muffler is provided both with asound deadening function for reducing air intake noise, and a waterseparation function for separating water from air. This obviates theneed to provide individual members respectively having a sound deadeningfunction and a water separation function, and accordingly the outboardmotor can be made smaller (more compact).

In the invention according to the fourth aspect, the silencer isdisposed downstream of the interference-type muffler, and upstream ofthe throttle body. With this arrangement, air intake noise can bereduced by the silencer, allowing air intake noise to be reduced evenmore.

In the invention according to the fifth aspect, air drawn in through theintake openings is guided in a vertical direction (downward) by the airintake guide section, and the air guided in the vertical direction bythe air intake guide section is then guided to a lateral direction bythe duct. A flow of air that has been guided laterally by the duct isimpeded by the separation ribs.

Impeding the flow of air using the separation ribs causes water that hasbeen guided together with air to collide with the separation ribs.Through collision of water against the separation ribs, the water can bemade to drip downward along the separation ribs. The water that has beendrawn in together with air can thus be reliably separated by theseparation ribs.

In the invention according to the sixth aspect, the intake passage isprovided with a dual system having a first intake passage section and asecond intake passage section. Furthermore, a first duct section isdisposed in the first intake passage section, and a second duct sectionis disposed in the second intake passage section. Furthermore,separation ribs are respectively disposed in the engine cover in aregion opposing the first duct section, and in a region opposing thesecond duct section. Therefore, the flow of air guided through the firstintake passage section is impeded by the separation ribs, and waterinflowing into the first intake passage section can be separated fromthe air by the separation ribs. Likewise, the flow of air guided throughthe second intake passage section is impeded by the separation ribs, andwater inflowing into the second intake passage section can be separatedfrom the air by the separation ribs. This allows water that has beendrawn in together with air to be reliably separated by the separationribs.

In the invention according to the seventh aspect, a drain port isdisposed in the bottom section of the duct. With this arrangement, waterdripping downward along the separation ribs can be collected in thebottom section, and the water collecting in the bottom section can bedrained to the outside through the drain port.

In the invention according to the eighth aspect, a guide rib is disposedin the duct, and air is guided towards the separation rib by this guiderib. Therefore, air directed into the duct can be guided towards theseparation rib satisfactorily, and water introduced together with theair can be made to suitably collide with the separation rib. This allowsthe water that has been drawn in together with air to be separated bythe separation rib even more reliably.

In the invention according to the ninth aspect, the body section of thesilencer is disposed on the belt cover, and the cover section of thesilencer is disposed on the engine cover, which allows gaps forpreventing interference to be eliminated from between the engine coverand the silencer, and from between the belt cover and the silencer.Therefore, the gaps for preventing interference can instead be employedas space for increasing the capacity of the silencer. This makes itpossible to increase the capacity of the silencer without increasing thesize of the engine cover, and sufficiently reduce air intake noise inthe intake passage.

Furthermore, the cover section of the silencer can be detached from thebody section from above. Therefore, the silencer chamber can be openedup by removing the cover section from the body section. This allows gritand dirt has infiltrated into the silencer chamber to be easilyeliminated without undue effort.

In the invention according to the tenth aspect, a sealing material isdisposed between the base section and the cover section. With thisarrangement, a reliable hermetic seal can be provided between the basesection and the cover section, and air intake noise in the intakepassage can be sufficiently reduced by the silencer.

In the invention according to the eleventh aspect, a tubular air intakeguide section is disposed in the intake passage, making it possible forwater to be separated from air by the air intake guide. Additionallyprovided is a guide bottom section having a downward pitch towards theintake openings from the air intake guide, a drain groove being disposedin the guide bottom section. Therefore, water that has been separated bythe air intake guide can be guided along the guide bottom section andinto the drain groove.

Furthermore, it is possible for water separated by the air intake guideto be guided towards the intake openings by the drain groove. Therefore,water that has been separated by the air intake guide is guided to theintake openings by the drain groove, and drained out from the enginecover through the intake openings. This allows water drawn in throughthe intake openings together with air to be reliably separated from theair.

In the invention according to the twelfth aspect, the drain groove isformed to have a downward pitch towards the intake openings from theintake guide section. Therefore, water separated by the air intake guideis guided towards the intake openings satisfactorily by the draingroove. This allows the water separated by the air intake guide to bereliably drained out from the engine cover through the intake openings.

In the invention according to the thirteenth aspect, the height of theouter groove wall of the drain groove is greater than the height of theinner groove wall. Therefore, water inside the drain groove can belargely isolated from air flowing above the drain groove, whereby thewater inside the drain groove can be prevented from splashing outtherefrom due to the air flowing thereabove. This allows water insidethe drain groove to be guided satisfactorily towards the intakeopenings, and reliably drained out from the engine cover through theintake openings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of an outboard motor according to an embodiment ofthe present invention;

FIG. 2 is a perspective view of an engine cover shown in FIG. 1;

FIG. 3 is a cross sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is an enlarged view of area 4 in FIG. 3;

FIG. 5 is an exploded cross sectional view of the outboard motor shownin FIG. 3;

FIG. 6 is a cross sectional view taken along line 6-6 in FIG. 4;

FIG. 7 is a perspective view of an exhaust fan chamber and an exhaustfan shown in FIG. 4;

FIG. 8 is a perspective view of an air intake means (an air guide and arear duct) shown in FIG. 3;

FIG. 9 is an exploded perspective view of the air intake means shown inFIG. 8;

FIG. 10 is a cross sectional view taken along line 10-10 in FIG. 1;

FIG. 11 (a) is a cross sectional view taken along line 11 a-11 a in FIG.10;

FIG. 11 (b) is an enlarged view of area 11 b in FIG. 11 (a);

FIG. 12 is a cross sectional view taken along line 12-12 in FIG. 10;

FIG. 13 is a perspective view of the rear duct shown in FIG. 9;

FIG. 14 is a cross sectional view taken along line 14-14 in FIG. 1;

FIG. 15 is a view taken in the direction of arrow 15 in FIG. 13;

FIG. 16 is a cross sectional view taken along line 16-16 in FIG. 2;

FIG. 17 is an exploded cross sectional view of a silencer shown in FIG.3;

FIG. 18 is a cross sectional view taken along line 18-18 in FIG. 1;

FIG. 19 is a diagrammatical view illustrative of the manner in which airinside the engine cover is discharged to the outside by exhaust meansaccording to the present embodiment;

FIG. 20( a) and FIG. 20( b) are views illustrative of the manner inwhich water is drained out from the engine cover via a drain groove ofthe air intake means shown in FIG. 8;

FIG. 21 is a view illustrative of the manner in which water directedinto the drain groove shown in FIGS. 20( a) and 20(b) is prevented fromsplashing;

FIG. 22( a) and FIG. 22B are views illustrative of the manner in whichwater is separated from air by a separation rib of adischarging/interference-type muffing means shown in FIG. 7;

FIG. 23( a) and FIG. 23( b) are views illustrative of the manner inwhich air is directed into a throttle body; and

FIG. 24( a) and FIG. 24( b) are views illustrative of the manner inwhich air intake noise is reduced by the silencer and thedischarging/interference-type muffler means (one of theinterference-type muffler sections).

DESCRIPTION OF EMBODIMENT

A certain preferred embodiment of the present invention will bedescribed in detail below with reference to the attached drawings.

Embodiment

As shown in FIG. 1, an outboard motor 10 includes an outboard motor body12, and attachment means 16 disposed on the outboard motor body 12 andcapable of being detachably attached to a hull 14 (in more specificterms, to a stern 15) of a boat. The attachment means 16 includes aswivel shaft 17 about which the outboard motor body 12 can swinglaterally (horizontally), and a tilt shaft 18 about which the outboardmotor body 12 can swing vertically.

The outboard motor body 12 includes a mount case 21 disposed on theattachment means 16, an engine 23 installed in the upper part of themount case 21, an engine cover 24 covering the engine 23, a drive shaft28 coaxially connected to a crankshaft 27 of the engine 23, a gearmechanism 29 to which rotation of the engine 23 (crankshaft 27) istransmitted via the drive shaft 28, and a propeller 32 to which rotationof the gear mechanism 29 is transmitted via a propeller shaft 31.

The outboard motor body 12 is further provided with exhaust means(venting means) 51 for discharging air inside the engine cover 24 to theoutside 35, and air intake means 52 for guiding air into the engine 23from the outside 35 of the engine cover 24.

The drive shaft 28 is covered by an extension case 33 disposed below themount case 21. The gear mechanism 29 and the propeller shaft 31 arecovered by a gear case 34 disposed below the extension case 33.

The engine 23 includes a cylinder block 36 constituting an engine body,a head cover 37, the crankshaft 27, cylinders 38, pistons 39, and thelike, and is further provided with auxiliary machinery 41 of the engine23.

By driving the engine 23 in this outboard motor 10, the rotation of theengine 23 is transmitted to the propeller 32 through the drive shaft 28,the gear mechanism 29, and the propeller shaft 31, rotating thepropeller 32 to propel the hull 14.

As shown in FIG. 2, the engine cover 24 has an exhaust opening 25 formedin an upper section 24 a, and intake openings 26 formed in both lateralsides 24 b. Only one intake opening 26 is shown in FIG. 2, and the otherintake opening 26 (on the far side) is shown in FIG. 10. The exhaustopening 25 and the intake openings 26 shall be described in detailbelow.

As shown in FIG. 3, the auxiliary machinery 41 of the engine 23 includesa throttle body 42 communicating with combustion chambers of the engine23; a generator 43 disposed to the opposite side of the throttle body42; and an exhaust fan 54 disposed between the generator 43 and thethrottle body 42.

As shown in FIG. 4, a drive belt 49 is looped around a driving pulley 48and a driven pulley 47 of the generator 43. The driving pulley 48 isdisposed at an upper end section 27 a of the crankshaft 27.Consequently, the driving pulley 48 rotates through rotation of thecrankshaft 27. Rotation of the driving pulley 48 is transferred to thedriven pulley 47 via the drive belt 49. The generator 43 is driventhrough rotation of the driven pulley 47.

As shown in FIGS. 4 and 5, the exhaust means 51 includes the exhaust fan54 coaxially disposed on the upper section of the driving pulley 48; abelt cover 55 covering a top of the drive belt 49; a fan cover 56disposed above the belt cover 55; and an exhaust passage 59 for guidingair inside the engine cover 24 to the outside.

The exhaust fan 54 is coaxially disposed on an upper section of thedriving pulley 48. Consequently, the exhaust fan 54 is caused to rotatethrough rotation of the driving pulley 48. The exhaust fan 54 dischargesair inside the engine cover 24 to the outside 35 of the engine cover 24.

The belt cover 55 is disposed covering the top of the drive belt 49, aswell as covering a top of part of the generator 43. Moreover, a rear endsection 55 a of the belt cover 55 is disposed to the throttle body 42side (FIG. 3). By disposing the belt cover 55 inside the engine cover24, the inside of the engine cover 24 is partitioned into an enginecompartment 61 and an intake/exhaust chamber 62.

The engine compartment 61 is formed below the belt cover 55, and housesthe engine 23. The intake/exhaust chamber 62 includes the exhaustpassage 59 and an intake channel or passage 73 that are formed above thebelt cover 55 (FIG. 3). The engine compartment 61 and the intake/exhaustchamber 62 communicate with one another.

The fan cover 56 is disposed on an upper side of the belt cover 55. Thefan cover 56 includes a first fan cover 57 disposed on the upper side ofthe belt cover 55, and a second fan cover 58 disposed on the upper sideof the first fan cover 57. Disposing the first fan cover 57 on the upperside of the belt cover 55, and the second fan cover 58 on the upper sideof a front section of the first fan cover 57 causes an exhaust fanchamber 64 to be formed by the belt cover 55 and the first and secondfan covers 57, 58.

Being disposed above the engine 23, the belt cover 55 and the fan cover56 may be disposed independently from the engine 23. Consequently, it ispossible to decide upon any desired shape for the belt cover 55 and thefan cover 56 irrespective of the contours of the engine 23. In so doing,it is possible to select any desired shape for the belt cover 55 and thefan cover 56, and therefore gaps and irregularities can be eliminatedfrom the exhaust fan chamber 64.

So eliminating gaps and irregularities from the exhaust fan chamber 64allows the exhaust fan chamber 64 to be tailored to a shape allowing theperformance of the exhaust fan 54 to be fully realized. Consequently,air in the intake/exhaust chamber 62 can be efficiently drawn into theexhaust fan chamber 64, and the air drawn into the exhaust fan chamber64 can be efficiently discharged to the outside of the exhaust fanchamber 64. Furthermore, the air discharged to the outside of theexhaust fan chamber 64 can be efficiently discharged to the outside 35of the engine cover 24.

Furthermore, the exhaust fan chamber 64 is disposed above the belt cover55, while the drive belt 49 and the driving pulley 48 are disposed belowthe belt cover 55. Consequently, the exhaust fan chamber 64 can bepartitioned off from the drive belt 49 and the driving pulley 48 by thebelt cover 55.

Partitioning off the exhaust fan chamber 64 from the drive belt 49 andthe driving pulley 48 prevents the flow of air drawn into the exhaustfan chamber 64 from being disturbed by the rotation of the drive belt 49or of the driving pulley 48. This allows the air in the intake/exhaustchamber 62 to be discharged to the outside of the engine cover 24 evenmore efficiently.

The second fan cover 58 is disposed higher than the first fan cover 57by H1. Consequently, a step H1 is provided in the fan cover 56 by thefirst fan cover 57 and the second fan cover 58. The exhaust fan chamber64 is partitioned off from the engine compartment 61 and theintake/exhaust chamber 62. As shown in FIG. 6, the exhaust fan 54 isrotatably housed in the exhaust fan chamber 64. The rotation of theexhaust fan 54 in the exhaust fan chamber 64 causes air in the exhaustfan chamber 64 to be directed into an exhaust port 66 as shown by thearrow.

As shown in FIGS. 4 and 7, an air intake port 65 through which theintake/exhaust chamber 62 communicates with the exhaust fan chamber 64is formed in the first and second fan covers 57, 58. The air intake port65 has a first air intake port 65 a formed at the approximate center 57a of the first fan cover 57, and a second air intake port 65 b formed ina front section 58 a of the second fan cover 58. The first and secondair intake ports 65 a, 65 b are disposed above the exhaust fan 54.

The step H1 is thus provided between the first fan cover 57 and thesecond fan cover 58, and the first and second air intake ports 65 a, 65b are disposed in the first and second fan covers 57, 58. Consequently,the exhaust fan chamber 64 is formed into a scroll shape (volute shape)as shown by the arrow. By adopting a scroll shape for the exhaust fanchamber 64, air can be drawn smoothly into the exhaust fan chamber 64through the first and second air intake ports 65 a, 65 b.

The exhaust port 66, through which the exhaust fan chamber 64communicates with the exhaust passage 59, is formed in a front section57 b of the first fan cover 57. The exhaust passage 59 is formed alongan upper section 24 a of the engine cover 24 by the upper section 24 aof the engine cover 24 and a front half section 71 a of an air guide 71.

The exhaust passage 59 communicates with the outside 35 of the enginecover 24 through the exhaust opening 25. As mentioned above, the exhaustopening 25 is formed in the upper section 24 a of the engine cover 24.Specifically, the exhaust fan chamber 64 communicates with the outside35 of the engine cover 24 through the exhaust port 66, the exhaustpassage 59, and the exhaust opening 25.

Due to rotation of the exhaust fan 54, the air in the intake/exhaustchamber 62 is drawn through the air intake port 65 and into the exhaustfan chamber 64. The air having been drawn into the exhaust fan chamber64 is then directed through the exhaust port 66 and to the outside ofthe exhaust fan chamber 64 (specifically, into the exhaust passage 59).The air having been directed into the exhaust passage 59 is thendischarged to the outside 35 of the engine cover 24 from the exhaustopening 25, through the exhaust passage 59.

As mentioned above, the intake/exhaust chamber 62 communicates with theengine compartment 61. Consequently, the air in the intake/exhaustchamber 62, as well as the air in the engine compartment 61, is reliablydischarged to the outside 35 of the engine cover 24 through rotation ofthe exhaust fan 54.

Furthermore, the exhaust fan chamber 64 has been formed to a scrollshape by providing the step H1 in the fan cover 56. By adopting a scrollshape for the exhaust fan chamber 64, the air in the intake/exhaustchamber 62 can be more smoothly drawn into the exhaust fan chamber 64through the first and second air intake ports 65 a, 65 b.

Consequently, the air in the intake/exhaust chamber 62 can be moresmoothly discharged to the outside 35 of the engine cover 24. Thisallows the air in the intake/exhaust chamber 62, as well as in theengine compartment 61, to be efficiently discharged to the outside 35 ofthe engine cover 24 through the intake/exhaust chamber 62. Consequently,the air (air temperature) inside the intake/exhaust chamber 62 and inthe engine compartment 61 can be kept at appropriate temperature.

In the outboard motor, typically, the auxiliary machinery 41, such asthe throttle body 42, the generator 43, and so on, is disposed on theupper side of the engine body. Air superheated by the engine 23 collectsin the upper section of the engine cover 24. Consequently, by providingthe upper section of the engine cover 24 with the air intake port 65 andthe exhaust port 66, air (superheated air) that has collected in thespace in the upper section of the engine cover 24 (specifically, in theintake/exhaust chamber 62) can be quickly discharged (eliminated) duringa hot restart.

This allows the cooling efficiency of the auxiliary machinery 41disposed above the engine 23 and below the belt cover 55 to beincreased. Herein, a hot restart refers to a restart of the engine 23after the engine 23 has been stopped, but before the engine 23 hascooled down.

Additionally, by providing the exhaust port 66 above the exhaust fan 54,air can be discharged upwardly through the exhaust port 66. Furthermore,by providing the exhaust passage 59 in the upper section 24 a of theengine cover 24, the exhaust passage 59 can be disposed above theexhaust port 66.

Consequently, air discharged upwardly through the exhaust port 66 can bedirected smoothly into the exhaust passage 59. This allows air to bedischarged more smoothly to the outside 35 of the engine cover 24through the exhaust opening 25 in the upper section 24 a of the enginecover 24.

As shown in FIGS. 8 and 9, the air intake means 52 includes the intakepassage 73 for guiding air into the throttle body 42 from the outside ofthe engine cover 24, a discharging/interference-type muffler means(interference-type muffler) 75 disposed partway along the intake passage73, and a silencer 77 disposed downstream of thedischarging/interference-type muffler means 75 and upstream of thethrottle body 42.

The intake passage 73 is a passage through which air drawn inside theengine cover 24 through the intake openings 26 at both lateral sides ofthe engine cover 24 can be introduced into the throttle body 42. Theintake passage 73 is formed, inter alia, by the engine cover 24, the airguide 71, and a rear duct 72. This intake passage 73 includes dualsystem passage sections having a pair of intake passage sections 73A,73B (a first intake passage section 73A and a second intake passagesection 73B). The first and second intake passage sections 73A, 73B areshown by arrows in FIG. 9.

The first intake passage section 73A guides air into the throttle body42 through one intake opening 26 of the intake openings 26 provided atboth lateral sides of the engine cover 24. The first intake passagesection 73A is provided with a first interference-type muffler section75A (see FIG. 16) disposed partway along the first intake passagesection 73A, and with the silencer 77 which is disposed downstream ofthe first interference-type muffler section 75A and upstream of thethrottle body 42.

The second intake passage section 73B guides air into the throttle body42 through the other intake opening 26 of the intake openings 26provided at both lateral sides of the engine cover 24. The second intakepassage section 73B is provided with a second interference-type mufflersection 75B (see FIG. 16) disposed partway along the second intakepassage section 73B, and with the silencer 77 which is disposeddownstream of the second interference-type muffler section 75B andupstream of the throttle body 42. The silencer 77 is employed (usedconcomitantly) by both the first intake passage section 73A and thesecond intake passage section 73B.

Consequently, air intake noise in the first intake passage section 73Acan be reduced by the first interference-type muffler section 75A (seeFIG. 16) and the silencer 77. Furthermore, air intake noise in thesecond intake passage section 73B can be reduced by the secondinterference-type muffler section 75B (see FIG. 16) and the silencer 77.This allows air intake noise produced during driving of the engine 23 tobe sufficiently reduced. The discharging/interference-type muffler means75 (the first interference-type muffler section 75A and the secondinterference-type muffler section 75B) and the silencer 77 shall bedescribed in detail below.

As shown in FIGS. 3 and 5, the air guide 71 is arranged to the upperside of the fan cover 56 and the rear duct 72, and disposed at the backsurface side of the upper section 24 a of the engine cover 24. The airguide 71 includes a guide bottom section 81 covering the fan cover 56and the rear duct 71, a passage inlet portion 82 disposed in a front endsection of the guide bottom section 81, a side wall 83 (see also FIG. 9)for the exhaust passage 59, disposed to the rear of the passage inletport 82; and first and second guide panels 84, 85 disposed inside theexhaust passage 59. The passage inlet port 82 is a region that forms theinlet port of the exhaust passage 59.

The exhaust passage 59 between the engine cover 24 and the front halfsection 71 a of the air guide 71 is formed by covering a space betweenthe guide bottom section 81 and the upper section 24 a of the enginecover 24, with the side wall 83 of the exhaust passage 59. By providingthe first and second guide panels 84, 85 in the exhaust passage 59, airdirected into the exhaust passage 59 from the exhaust fan chamber 64 canbe guided smoothly towards the exhaust opening 25 by the guide panels84, 85.

As shown in FIG. 10, the air guide 71 is further provided with an airintake guide section 87 disposed in a rear end section of the guidebottom section 81, a drain groove 91 disposed to extend frontward fromthe outside perimeter of the air intake guide section 87, and aplurality of guide plates 95 disposed to the outside of the drain groove91. The plurality of guide plates 95 is disposed in regionscorresponding to the intake openings 26 at both sides, and is designedto separate water from the air drawn in through the intake openings 26.

It may occur that, as air is drawn inside the engine cover 24 throughthe intake openings 26, spray, or drops of water that have collectedaround the intake openings 26, could get drawn inside the engine cover24 together with the air. Therefore, the water drawn in together withair through the intake openings 26 can be separated from the air bycolliding against the plurality of guide plates 95.

Here, the openings of the intake openings 26 have been determined insuch a way that the air intake resistance is not increased by theplurality of guide plates 95. The air directed inside the engine cover24 through the intake openings 26 is directed approximately horizontallyalong the guide bottom section 81, to the air intake guide section 87.

As shown in FIGS. 3 and 10, the air intake guide section 87 is formedpartway along the intake passage 73. This air intake guide section 87 isa tubular passage disposed facing in a vertical direction in a rear endsection of the guide bottom section 81, and having an air intake port 87b disposed at an upper end section 87 a thereof. The rear end section ofthe guide bottom section 81 is a region through which air drawn inthrough the intake openings 26 flows in an approximately horizontaldirection as shown by the arrows (see FIG. 10).

The air intake port 87 b of the air intake guide section 87 is arrangedabove the guide bottom section 81. The space above the guide bottomsection 81 communicates with the space below the guide bottom section 81through this air intake guide section 87. Consequently, air drawn inthrough the intake openings 26 is drawn inside the air intake guidesection 87 through the air intake port 87 b of the air intake guidesection 87, whereby the air can be guided downwardly (in a verticaldirection) as shown by the arrows (see FIG. 3).

Furthermore, by disposing the air intake guide section 87 to face in avertical direction in the rear end section of the guide bottom section81, the direction of flow of air drawn in through the intake openings 26is redirected by the air intake guide section 87. At this time, watercontained in the air collides against the air intake guide section 87,so that the water can be separated from the air. Here, the shape of theair intake guide section 87 has been determined in such a way that theair intake resistance is not increased by the air intake guide section87.

Specifically, the air intake guide section 87 is designed with thecapability to separate water from air drawn inside the engine cover 24through the intake openings 26. The water separated by the air intakeguide section 87 is directed into a rear drain groove section 92(discussed below) and the guide bottom section 81.

The guide bottom section 81 is formed to have a downward pitch of aslope angle θ1 (see FIG. 12) going towards the front edge 81 b from arear edge 81 a thereof (FIG. 10). Furthermore, the guide bottom section81 is formed to have a downward pitch of a slope angle θ2 (see FIG. 11)towards both lateral sides from a widthwise center 81 c thereof.Specifically, between the intake openings 26 and the air intake guidesection 87, the guide bottom section 81 is formed to a sloped profile ofdownward pitch towards the intake openings 26 from the air intake guidesection 87.

The drain groove 91 is disposed in the guide bottom section 81. Thedrain groove 91 has the rear drain groove section 92, which is disposedin a rear section of the air intake guide section 87, and side draingroove sections 93 at both sides, extending frontward through both sidesof the air intake guide section 87. This drain groove 91 is designedsuch that it is possible for water separated from air in the air intakeguide section 87 to drain to the outside 35 of the engine cover 24through the intake openings 26.

The rear drain groove section 92 is disposed in a rear section of theair intake guide section 87, and like the guide bottom section 81, isformed to have a downward pitch of a slope angle θ2 (see FIG. 11)towards both lateral sides from a widthwise center 92 a thereof.Consequently, water separated from air in the air intake guide section87 can be guided into both outside edge sections 92 b of the rear draingroove section 92, as shown by the arrows.

The side drain groove sections 93 situated at both sides extendfrontward to the approximate center of the intake openings 26 in thelongitudinal direction, from both outside edge sections 92 b of the reardrain groove section 92. Specifically, in the side drain groove sections93, rear edge sections 93 a communicate with the outside edge sections92 b of the rear drain groove section 92, while front end sections 93 bare positioned in the approximate center of the intake openings 26 inthe longitudinal direction. Consequently, water that has been directedinto the rear drain groove section 92 after being separated in the airintake guide section 87 is guided into the side drain groove sections 93from the rear edge sections 93 a of the side drain groove sections 93.

The side drain groove sections 93 are disposed to the outside of thewidthwise center 81 c. Furthermore, the guide bottom section 81 isformed to have a downward pitch of a slope angle θ2 (see FIG. 11)towards both sides from the widthwise center 81 c. Consequently, waterthat has been separated in the air intake guide section 87 and directedinto the guide bottom section 81 is guided into the side drain groovesections 93 from the rear edge sections 93 a of the side drain groovesections 93.

As shown in FIGS. 10 and 12, the side drain groove sections 93 extendfrontward from the outside edge sections 92 b of the rear drain groovesection 92, and thereby, like the guide bottom section 81, are formed tohave a downward pitch of a slope angle θ1 (see FIG. 12) towards theintake openings 26 from the air intake guide section 87. Consequently,water inside the side drain groove sections 93 can be guided towards thefront end sections 93 b from the rear end sections 93 a.

As mentioned above, the front end sections 93 b of the side drain groovesections 93 are positioned in the approximate center of the intakeopenings 26 in the longitudinal direction. Consequently, water directedinto the side drain groove sections 93 from the rear drain groovesection 92 and the guide bottom section 81 is guided towards the intakeopenings 26 through the side drain groove sections 93. In so doing,water that has been separated in the air intake guide section 87 isreliably drained to the outside 35 of the engine cover 24 through theintake openings 26.

As shown in FIG. 11 (a), the side drain groove sections 93 have an outergroove wall 97 disposed closer, towards the intake openings 26, an innergroove wall 98 disposed further away from the intake openings 26, and aslot bottom section 99 connecting the inner groove wall 98 and the outergroove wall 97 at the bottom end. The side drain groove sections 93 areformed to a generally “U” shaped cross section defined by the innergroove wall 98, the outer groove wall 97, and the slot bottom section99.

Like the guide bottom section 81, the slot bottom section 99 is formedto have a downward pitch of a slope angle θ2 towards the outside in thewidth direction of the guide bottom section 81 (specifically, towardsthe plurality of guide plates 95 (FIG. 10)). In the side drain groovesections 93, the height H2 of the outer groove wall 97 is greater thanthe height H3 of the inner groove wall 98. Consequently, the outergroove wall 97 is taller by a height H4 (H2-H3) in relation to the innergroove wall 98. The reason for making the outer groove wall 97 taller bythe height H4 than the inner groove wall 98 shall be described in detailbelow.

As shown in FIG. 12, the side drain groove sections 93 are formed tohave a progressively shallower slot depth going from the air intakeguide section 87 towards the front end sections 93 b. By adoptingprogressively shallower slot depths for the side drain groove sections93, the height H2 of the outer groove wall 97 (FIG. 11 (b)) becomesprogressively shorter going from the air intake guide section 87 towardsthe front end sections 93 b.

Thus, the side drain groove sections 93 are formed to have a downwardpitch of a slope angle θ1 towards the intake openings 26 from the airintake guide section 87, and the height H2 of the outer groove wall 97(FIG. 11 (b)) is progressively less from the air intake guide section 87towards the front end sections 93 b. Consequently, water inside the sidedrain groove sections 93 can be reliably guided from the rear endsections 93 a towards the front end sections 93 b.

The water that has been guided to the front end sections 93 b drains asshown by the arrows in FIG. 10, from the front end sections 93 b to theoutside 35 of the engine cover 24 through the plurality of guide plates95 and the intake openings 26. This allows water that has been drawn intogether with air through the intake openings 26 to be reliablyseparated from the air.

The reason for making the outer groove wall 97 shown in FIG. 11 (b)taller by the height H4 than the inner groove wall 98 shall be describedhere. As shown in FIGS. 10 and 11 (a), air drawn in towards the airintake guide section 87 from the intake openings 26 flows above the sidedrain groove sections 93 so as to cross the side drain groove sections93, as shown by the arrows. Therefore, it may occur that the waterinside the side drain groove sections 93 could be caused to splashoutside the side drain groove sections 93 by air flowing above the sidedrain groove sections 93.

As shown in FIG. 11 (b), the outer groove wall 97 is higher than theinner groove wall 98 by height H4. Consequently, water 101 inside theside drain groove sections 93 can be largely isolated from air flowingabove the side drain groove sections 93 as shown by the arrow. Thisallows the water 101 inside the side drain groove sections 93 to beprevented from splashing to the outside of the side drain groovesections 93 due to air flowing above the side drain groove sections 93.Consequently, the water 101 inside the side drain groove sections 93 canbe guided towards the intake openings 26 (specifically, into the frontend sections 93 b) and reliably drained to the outside 35 of the enginecover 24 through the intake openings 26.

As shown in FIG. 9, the rear duct 72 is disposed below a rear halfsection 71 b of the air guide 71. The rear duct 72 is disposeddownstream of the air intake guide section 87 and located near the rearwall 24 c of the engine cover 24 (see FIG. 8).

As shown in FIGS. 13 and 14, this rear duct 72 includes a mountingsection 104 onto which it is possible to mount the air intake guidesection 87 of the air guide 71 (FIG. 10), a vertical duct section (duct)105 suspended downward from a rear end section 104 a of the mountingsection 104, and side guide sections 107 extending frontward from bothsides of the vertical duct section 105.

The mounting section 104 is a region that covers the throttle body 42from above. This mounting section 104 has a mating wall section 111projecting upward from a rear half section 104 b, and a rear partitionwall 113 projecting in a vertical direction from a front edge 104 c(FIGS. 3, 4). The mating wall section 111 has a guide port 112 thatopens out in a rear end section thereof, and is designed to mate withthe air intake guide section 87 of the air guide 71.

When the air intake guide section 87 has been mated with the mating wallsection 111, the air intake guide section 87 communicates with thevertical duct section 105 through the guide port 112. Consequently, airdirected into the air intake guide section 87 is guided through theguide port 112 and downward along the vertical duct section 105.

As shown in FIGS. 13 and 15, the vertical duct section 105 is a duct ofvertical design provided with a center partition section 106 capable ofbisecting the vertical duct section 105 in a vertical direction, and apair of segmented duct sections (duct sections) 115 bisected by thecenter partition section 106.

As shown in FIG. 16, the vertical duct section 105 is covered by therear wall 24 c of the engine cover 24. When the vertical duct section105 is covered by the rear wall 24 c of the engine cover 24, thedischarging/interference-type muffler means 75 is formed by the verticalduct section 105 and the rear wall 24 c of the engine cover 24.

As shown in FIGS. 13 and 15, the center partition section 106 has anupper center partition section 106 a extending downward to a rectangularopening 109 from the rear end section 104 a of the mounting section 104,and a lower center partition section 106 b extending from therectangular opening 109 to a lower end section 105 a of the verticalduct section 105. By thus providing the center partition section 106 inthe vertical duct section 105, the vertical duct section 105 issegmented to either side of the center partition section 106.

By virtue of a bisected structure in which the vertical duct section 105is segmented to either side of the center partition section 106, thepair of segmented duct sections 115 is created in the vertical ductsection 105. In so doing, when air inside the air intake guide section87 is guided downwardly into the vertical duct section 105 through theguide port 112, the flow of air inside the air intake guide section 87gets divided between the pair of segmented duct sections 115 by thecenter partition section 106.

The segmented duct sections 115 include, in a duct of vertical design,an upper duct section 116 descending from the rear end section 104 a ofthe mounting section 104, and a lower duct section 117 descending from alower end section 116 a of the upper duct section 116.

In the upper duct sections 116, descending step sections 121 aredisposed to the sides of the center partition section 106, and guideribs 122 are disposed within the descending step sections 121.

The descending step sections 121 are formed to have a downward pitchtowards the guide ribs 122 from the center partition section 106.Consequently, air being guided downwardly into the upper duct sections116 is guided in lateral directions towards the guide ribs 122 by thedescending step sections 121, as shown by the arrows.

The guide ribs 122 are disposed in a vertical orientation in proximityto the sides of the upper duct sections 116, and project rearward fromthe upper duct sections 116. These guide ribs 122 are capable of guidingair directed into the upper duct sections 116 towards separation ribs123 as shown by the arrows (FIG. 14).

Here, as shown in FIGS. 2 and 14, the separation ribs 123 are disposedon rear wall 24 c of the engine cover 24 in regions 24 d thereof opposedto the upper duct sections 116. The separation ribs 123 are disposed tothe outside of the guide ribs 112, and project towards the upper ductsections 116. The separation ribs 123 are disposed in a verticalorientation substantially parallel to the guide ribs 122.

By thus providing the separation ribs 123 in proximity to either side ofthe upper duct sections 116, the flow of air guided laterally by theupper duct sections 116 is impeded by the separation ribs 123. Becausethe flow of air is impeded by the separation ribs 123, water present inthe air collides against the separation ribs 123, and the water can beseparated from the air.

Furthermore, the water that has been separated by the separation ribs123 can be made to drip downward along the separation ribs 123. Thisallows the water contained in the air to be reliably separated from theair by the separation ribs 123.

As shown in FIGS. 8 and 9, the intake passage 73 includes a dual systemhaving the first intake passage section 73A and the second intakepassage section 73B. Furthermore, the one segmented duct section 115 isdisposed in the first intake passage section 73A, while the othersegmented duct section 115 is disposed in the second intake passagesection 73B. Furthermore, on the engine cover 24, the separation ribs123 are disposed in a region opposed to the one segmented duct section115, and in a region opposed to the other segmented duct section 115.

Consequently, the flow of air guided into the first intake passagesection 73A is impeded by the separation rib 123, whereupon waterflowing into the first intake passage section 73A can be separated fromthe air by the separation rib 123. Likewise, the flow of air guided intothe second intake passage section 73B is impeded by the separation rib123, whereupon water flowing into the second intake passage section canbe separated from the air by the separation rib 123. This allows thewater drawn in together with the air to be reliably separated from theair by the separation ribs 123.

As shown in FIG. 14, the guide ribs 122 are disposed upstream of theseparation ribs 123. Consequently, air guided into the upper ductsections 116 can be guided satisfactorily towards the separation ribs123 by the guide ribs 122 as shown by the arrows, and water directed intogether with the air can be induced to collide in an appropriate manneragainst the separation ribs 123. This allows the water drawn in togetherwith the air to be reliably separated from the air by the separationribs 123. The shapes of the separation ribs 123 and the guide ribs 122have been determined in such a way that the air intake resistance is notincreased by the plurality of separation ribs 123 and guide ribs.

As shown in FIGS. 13 and 15, center protruding sections 126 thatprotrude rearward from the center in the width direction are disposed inthe lower duct sections 117, and ascending steps 128 are disposed atlocations to the outside of the center protruding sections 126 and abovea bottom section 127. Drain ports 129 are disposed at outside edgesections of the bottom section 127 (to the lower side of the ascendingsteps 128). The bottom section 127 is formed to have a downward pitch ofslope angle θ3 towards the outside from the center partition section106.

Specifically, the drain ports 129 are disposed in the lowermost sectionof the bottom section 127. The water separated from the air by theseparation ribs 123 (see also FIG. 14) drips down onto this bottomsection 127. Consequently, the water that has dripped down onto thebottom section 127 is guided along the bottom section 127 and into thedrain ports 129, and drains to the outside of the lower duct sections117 through the drain ports 129.

When the downward flow of air guided into the upper duct sections 116 isredirected laterally by the descending step sections 121 as shown by thearrows, some of the air is directed downwardly towards the lower ductsections 117 as shown by the arrows. The downwardly directed air risesalong the ascending steps 128 as shown by the arrows.

The side guide sections 107 have side partition walls 119 that extendfrontward to outside sections 77 a of the silencer 77 from outside loweredge sections 116 b of the upper duct sections 116, and that projectupward from front end sections 107 b.

One of the side guide sections 107 forms part of the first intakepassage section 73A (FIG. 9). The other side guide section 107 formspart of the second intake passage section 73B. The following descriptionrelates to the one side guide section 107 only, omitting description ofthe other side guide section 107.

The side guide section 107 communicates at a rear end section 107 athereof with the descending step section 121, and at a front end section107 b communicates with an inlet port 136 of the silencer 77.

The side partition wall 119 is disposed at predetermined spacing awayfrom the rear partition wall 113. Furthermore, the upper end of the sidepartition wall 119 and the upper end of the rear partition wall 113 abutthe back surface of the guide bottom section 81 (FIG. 4). Consequently,the inlet port 136 of the silencer 77 is formed between the sidepartition wall 119 and the rear partition wall 113.

The front end section 107 b of the side guide section 107 communicateswith the inlet port 136. Consequently, the air from which water has beenseparated by the separation rib 123 of the upper duct section 116 isdirected into the side guide section 107 as shown by the arrows. The airdirected into the side guide section 107 is directed through the sideguide section 107 and into a silencer chamber 135 from the inlet port136 of the silencer 77 as shown by the arrows.

Meanwhile, air directed downward into the lower duct section 117 risesalong the ascending step 128 as shown by the arrows. The rising air isdirected into the side guide section 107 as shown by the arrows. The airdirected into the side guide section 107 is directed through the sideguide section 107 and into the silencer chamber 135 from the inlet port136 of the silencer 77 as shown by the arrows.

As shown in FIGS. 13 and 14, the interference-type muffler section 75Ais formed by the segmented duct section 115, in combination with therear wall 24 c of the engine cover 24. The interference-type mufflersection 75A includes a function of reducing air intake noise transmittedfrom the inlet port 136 of the silencer 77. The interference-typemuffler section 75A shall be discussed in detail below.

As shown in FIG. 4, the silencer 77 includes a body section 132 formedby a rear section 55 b of the belt cover 55, and a rear section of thefan cover 56, and a cover section 133 formed above the body section 132.The silencer 77 includes the silencer chamber 135.

As shown in FIG. 17, the body section 132 is formed by the rear section55 b of the belt cover 55, and the rear section of the fan cover 56 (arear section 57 c of the first fan cover 57 and a rear section 58 b ofthe second fan cover 58). Specifically, the belt cover 55 and the fancover 56 are disposed in the body section 132. This body section 132includes a lower half chamber (silencer lower half chamber) 135 a of thesilencer chamber 135 (see FIG. 4).

In the body section 132, openings 138 to the silencer lower half chamber135 a are formed in both sides of the second fan cover 58 (rear section58 b) (FIGS. 13, 14), and an outlet port 139 is formed in a rear endsection. The outlet port 139 is formed by the rear section 55 b of thebelt cover 55 and the rear section 58 b of the second fan cover 58. Thisoutlet port 139 communicates with the throttle body 42 through acommunicating passage 141.

The cover section 133 is formed above the body section 132. The coversection 133 is formed by the second fan cover 58, the guide bottomsection 81, a front partition wall 144, the rear partition wall 113, anda sealing material 143.

As shown in FIGS. 12 and 14, the sealing material 143 is formed into aframe shape that is substantially pentagonal in plan view and isdisposed on the upper surface of the second fan cover 58 (the rearsection 58 b). As shown in FIG. 4, a front half section 143 a of thesealing material 143 is pressed from above by the lower end of the frontpartition wall 144. The front partition wall 144 is a projecting piecethat projects downward from the back surface of the guide bottom section81. Furthermore, a rear half section 143 b of the sealing material 143(see also FIGS. 12 and 14) is pressed from above by the lower end of therear partition wall 113. The rear partition wall 113 at its upper endabuts the back surface of the guide bottom section 81.

Through pressing of the front half section 143 a of the sealing material143 by the front partition wall 144, and pressing of the rear halfsection 143 b of the sealing material 143 by the rear partition wall113, the cover section 133 of the silencer 77 is formed by the secondfan cover 58, the front partition wall 144, the rear partition wall 113,and the guide bottom section 81.

As shown in FIG. 17, the guide bottom section 81 (specifically, the airguide 71) is disposed on the engine cover 24. Consequently, the coversection 133 is disposed on the body section 132 so as to permitdetachment from above. This cover member 133 includes an upper halfsection (silencer upper half chamber) 135 b of the silencer 135 (FIG.4). The silencer upper half chamber 135 b and the silencer lower halfchamber 135 a communicate through the openings 138 (FIG. 14).

In this silencer 77, the inlet port 136 (FIG. 14) communicates with theside guide section 107, and the outlet port 139 communicates with thethrottle body 42 via the communicating passage 141. Consequently, asshown in FIG. 14, air directed into the side guide section 107 from theinlet port 136 as shown by the arrows is directed from the inlet port136 into the silencer upper half chamber 135 b (FIG. 4) as shown by thearrows. The air directed into the silencer upper half chamber 135 b isdirected through the openings 138 and into the silencer lower halfchamber 135 a as shown by the arrows.

As shown in FIG. 18, the air directed into the silencer lower halfchamber 135 a is directed into the throttle body 42 through the outletport 139 and the communicating passage 141. The throttle body 42communicates with the combustion chamber of the engine 23. When airintake noise is produced along with air intake pulsations and shockwaves when the engine 23 is being driven, this silencer 77 includes thefunction of reducing the air intake noise produced thereby.

As shown in FIG. 4, in the silencer 77, the body section 132 is disposedon the belt cover 55 and the fan cover 56, and the cover section 133 isdisposed on the engine cover 24. The reason for disposing the bodysection 132 on the belt cover 55, and for disposing the cover section133 on the engine cover 24, shall be described below.

In an ordinary outboard motor, the silencer is disposed between theengine cover and the belt cover. In cases in which the silencer isdisposed between the engine cover and the belt cover, it may occur thatthe silencer could interfere with the engine cover and the belt cover.For this reason, it is necessary to provide a gap between the enginecover and the silencer, and between the belt cover and the silencer, inorder to prevent interference by the silencer.

By contrast, in the outboard motor 10 of the present embodiment, thebody section 132 of the silencer 77 is disposed on the belt cover 55 andthe fan cover 56, while the cover section 133 of the silencer 77 isdisposed on the engine cover 24. Consequently, gaps for preventinginterference can be eliminated from between the engine cover 24 and thesilencer 77, and from between the belt cover 55 (including the fan cover56) and the silencer 77.

This allows gaps for preventing interference to be repurposed as spacefor increasing the capacity of the silencer 77. Consequently, it ispossible to increase the capacity of the silencer 77 without making theengine cover 24 larger, and air intake noise in the intake channel 73(air intake noise produced along with air intake pulsations and shockwaves) can be reduced to a sufficient extent.

Furthermore, as shown in FIG. 17, the cover section 133 of the silencer77 is disposed on the chassis section 132 so as to be detachabletherefrom from above. Consequently, the silencer chamber 135 (FIG. 4)can be opened up by detaching the cover section 133 from the bodysection 132. This allows grit and dust that has infiltrated into thesilencer chamber 135 to be easily eliminated without undue effort.

Still further, the sealing material 143 is disposed between the bodysection 132 and the cover section 133. This ensures a hermetic sealbetween the body section 132 and the cover section 133, and air intakenoise in the intake channel 73 (FIG. 9) can be sufficiently reduced bythe silencer 77.

Next, the discharging/interference-type muffler means 75 shall bediscussed in detail on the basis of FIGS. 13 and 16. As shown in FIGS.13 and 16, the discharging/interference-type muffler means 75 isdisposed in a vertical arrangement inside the engine cover 24, and, dueto being bisected in a vertical direction by the center partitionsection 106, includes the pair of interference-type muffler sections(side branches) 75A, 75B.

The one interference-type muffler section 75A is formed by the onesegmented duct section 115, and a region in the rear wall 24 c of theengine cover 24 which is opposed to the one segmented duct section 115.The interference-type muffler section 75A is disposed partway along thefirst intake passage section 73A (FIG. 9), and communicates with thethrottle body 42 through the silencer 77.

The other interference-type muffler section 75B is formed by the othersegmented duct section 115, and a region in the rear wall 24 c of theengine cover 24 which is opposed to the other segmented duct section115. The interference-type muffler section 75B is disposed partway alongthe second intake passage section 73B (FIG. 9), and communicates withthe throttle body 42 through the silencer 77. The throttle body 42communicates with the combustion chamber of the engine 23.

As shown in FIGS. 13 and 18, when air intake noise is produced alongwith air intake pulsations and shock waves while the engine 23 is beingdriven, the air intake noise produced thereby is directed from the inletports 136 of the silencer 77 to the side guide sections 107 as shown bythe arrows. The air intake noise directed into the side guide sections107 is directed from the side guide sections 107 into the upper ductsections 116 as shown by the arrows, and then guided into the lower ductsections 117 as shown by the arrows.

The air intake noise directed into the lower duct sections 117 istransmitted downward inside the lower duct sections 117 and reaches theascending steps 128 as shown by the arrows. The flow of air intake noisetransmitted to the ascending steps 128 is redirected upward through theascending steps 128 and the center protruding sections 126 as shown bythe arrows. At an interference position P1, the air intake noisedirected upward from the lower duct sections 117 interferes with the airintake noise that has been directed into the upper duct sections 116from the side guide sections 107.

At the interference position P1, the air intake noise directed into theupper duct sections 116 from the lower duct sections 117 (second airintake noise) undergoes inversion of the phase of its frequency withrespect to the air intake noise directed directly into the upper ductsections 116 from the side guide sections 107 (first air intake noise).

Specifically, the pair of interference-type muffler sections 75A, 75B isformed such that the phase of the frequency of the second air intakenoise is inverted with respect to that of the first air intake noise atthe interference position P1. In specific terms, the phase of thefrequency of the second air intake noise is inverted with respect tothat of the first air intake noise, through adjustments to the passagearea and the passage length for the first air intake noise and thesecond air intake noise. By so causing the phase-inverted second airintake noise to interfere with the first air intake noise at theinterference position P1, air intake noise transmitted from the inletport 136 of the silencer 77 can be reduced.

With the discharging/interference-type muffler means 75, it is possibleto attenuate the frequency band of air intake noise which, in exhaustnoise, is a component producing particularly high acoustic pressure. Inso doing, when air intake noise is produced along with air intakepulsations and shock waves while the engine 23 is being driven, the airintake noise can be sufficiently reduced by thedischarging/interference-type muffler means 75.

As shown in FIGS. 13 and 16, in the outboard motor 10, it is typical fordead space to be present between the side walls (particularly the rearwall 24 c) of the engine cover 24 and the engine 23. By providing thedischarging/interference-type muffler means 75 in a verticalarrangement, this dead space can be utilized for installation of thedischarging/interference-type muffler means 75. This obviates the needto ensure additional space for installation of thedischarging/interference-type muffler means 75, allowing the outboardmotor 10 to be made smaller (more compact).

Furthermore, the drain port 129 is provided in the bottom section 127 ofthe discharging/interference-type muffler means 75. Thedischarging/interference-type muffler means 75 is disposed in a verticalarrangement. Consequently, water that has been separated from air by thedischarging/interference-type muffler means 75 can be made to dripdownward to the bottom section 127. Furthermore, the water that hasdripped down to the bottom section 127 can be drained out from thedischarging/interference-type muffler means 75 through the drain port129. This allows air from which water has been separated by thedischarging/interference-type muffler means 75 to be guided into thethrottle body 42 (FIG. 18).

Specifically, the discharging/interference-type muffler means 75 isprovided both with a sound deadening function for reducing air intakenoise, and a water separation function for separating water from air.This obviates the need to provide individual members respectively havinga sound deadening function and a water separation function, andtherefore the outboard motor 10 can be made even smaller (more compact).

Next, an example in which air inside the engine cover 24 is dischargedto the outside 35 by the exhaust means (venting means) 51 shall bedescribed on the basis of FIG. 19. As shown in FIG. 19, a step H1 isprovided between the first fan cover 57 and the second fan cover 58. Thefirst air intake port 65 a is formed in the first fan cover 57, and thesecond air intake port 65 b is formed in the second fan cover 58.

Through rotation of the exhaust fan 54, the air in the intake/exhaustchamber 62 is directed along a scroll shaped (volute shaped) trajectoryinside the exhaust fan chamber 64, as shown by the arrows A. Bydirecting the air in the intake/exhaust chamber 62 along a scroll shapedtrajectory, the air in the intake/exhaust chamber 62 can be smoothly andefficiently drawn into the exhaust fan chamber 64.

The air drawn into the exhaust fan chamber 64 is directed through theexhaust port 66 and then outside the exhaust fan chamber 64(specifically, into the exhaust passage 59) as shown by arrow B. The airdirected into the exhaust passage 59 is then guided along the exhaustpassage 59 as shown by arrow D, passes through the exhaust passage 59,and is discharged to the outside 35 of the engine cover 24 through theexhaust opening 25 as shown by arrow E.

The intake/exhaust chamber 62 communicates with the engine compartment61. Consequently, air in the intake/exhaust chamber 62, and air in theengine compartment 61, can be reliably discharged to the outside 35 ofthe engine cover 24 through rotation of the exhaust fan 54. This allowsthe air temperature inside the intake/exhaust chamber 62 and in theengine compartment 61 to be kept at appropriate temperature.

Next, an example in which air drawn in from the outside 35 of the enginecover 24 is directed to the throttle body 42 (see FIG. 23 (b)) shall bedescribed on the basis of FIGS. 20 to 23. To facilitate understanding ofthe flow of air, only the first intake passage section 73A (see FIG. 9)is described in FIGS. 20 to 23.

Firstly, an example in which water is separated from air directed intothe air guide 71 through the intake opening 26 shall be described on thebasis of FIGS. 20 to 21. As shown in FIG. 20 (a), air is directedtowards the air guide 71 from the intake opening 26 of the engine cover24 as shown by arrow F.

The air drawn in from the intake opening 26 is directed inside theengine cover 24 through the plurality of guide plates 95. In theprocess, water contained in the air collides against the plurality ofguide plates 95, separating the water from the air. The air from whichthe water has been separated by the plurality of guide plates 95 isdirected along the guide bottom section 81 of the air guide 71, to theair intake guide section 87.

By directing the air to the air intake guide section 87, the air drawnin from the intake opening 26 is redirected upward by the air intakeguide section 87 as shown by arrow G. Consequently, the water containedin the air collides against the outside peripheral surface of the airintake guide section 87, separating the water from the air. The air fromwhich the water has been separated by the air intake guide section 87 isdrawn inside the air intake guide section 87 from the air intake port 87b of the air intake guide section 87. The air drawn inside the airintake guide section 87 is directed downward (in a vertical direction)as shown by arrow H.

As shown in FIG. 20 (b), the water separated from the air by the airintake guide section 87 drips down along the outside peripheral surfaceof the air intake guide section 87 and is directed into the rear draingroove section 92 and the side drain groove section 93 at either side.The water directed into the rear drain groove section 92 and the sidedrain groove section 93 at either side is guided along the side draingroove section 93 at either side to the front end section 93 b as shownby arrow I. The water guided to the front end section 93 b is drained tothe outside 35 of the engine cover 24 through the intake opening 26 fromthe front end section 93 b as shown by arrow J.

As shown in FIG. 21, the outer groove wall 97 is higher than the innergroove wall 98 by height H4. Air drawn in towards the air intake guidesection 87 from the intake opening 26 flows above the side drain groovesection 93 in such a way as to cross the side drain groove section 93,as shown by arrow K. Consequently, by making the outer groove wall 97higher than the inner groove wall 98 by height H4, water 101 inside theside drain groove section 93 can be largely isolated from the airflowing above the side drain groove section 93.

This allows the water 101 inside the side drain groove section 93 to beprevented from splashing to the outside of the side drain groove section93 due to the air flowing above the side drain groove section 93.Consequently, the water 101 inside the side drain groove section 93 canbe guided satisfactorily towards the front end section 93 b (FIG. 20(b)), and reliably drained to the outside 35 of the engine cover 24through the intake opening 26 (FIG. 20 (b)).

Next, an example in which water is separated from air directed into thesegmented duct section 115 of the discharging/interference-type mufflermeans 75 shall be described on the basis of FIGS. 22 and 23. As shown inFIG. 22 (a), air directed into the air intake guide section 87 (FIG. 20(a)) is directed through the guide port 112, and downward along theupper duct section 116 of the vertical duct section 105 as shown byarrow L. The air guided downward into the upper duct section 116 isguided laterally towards the guide rib 122 by the descending stepsection 121 as shown by arrow M.

As shown in FIG. 22 (b), the air guided towards the guide rib 122 isthen guided towards the separation rib 123 by the guide rib 122 as shownby arrow N. By guiding the air towards the separation rib 123, theairflow can be impeded by the separation rib 123. Having the flow of airimpeded by the separation rib 123 causes the water in the air to collideagainst the separation rib 123, separating the water from the air. Theair from which the water has been separated by the separation rib 123 isdirected towards the side guide section 107 as shown by arrow O.

Meanwhile, as shown in FIG. 22 (a), the water separated from the air bythe separation rib 123 drips down to the bottom section 127 as shown bythe arrows. The water dripping down to the bottom section 127 is guidedalong the bottom section 127 to the drain port 129, and drains tooutside the lower duct section 117 through the drain port 129.

As shown in FIG. 23 (a), some of the air guided downward into the upperduct section 116 as shown by arrow L is guided further downward into thelower duct section 117 as shown by arrow P. The downwardly guided airrises along the ascending step 128 as shown by arrow Q. The rising airis directed to the side guide section 107 as shown by arrow R.

The air directed to the side guide section 107 as shown by arrow O andthe air directed to the side guide section 107 as shown by arrow R isthen directed through the side guide section 107, and into the silencerupper half chamber 135 b of the silencer chamber 135 from the inlet port136 of the silencer 77 as shown by arrow S. The air directed into thesilencer upper half chamber 135 b is directed through the opening 138 ofthe silencer 77 and into the silencer lower half chamber 135 a as shownby arrow T.

As shown in FIG. 23 (b), the air directed into the silencer lower halfchamber 135 a is then directed towards the outlet port 139 of thesilencer chamber 135 as shown by arrow U. The air directed towards theoutlet port 139 of the silencer chamber 135 is then directed to thethrottle body 42 through the communicating passage 141 as shown by arrowV.

As described in FIGS. 20 to 23, by virtue of the plurality of guideplates 95, the air intake guide section 87, and the separation rib 123provided on the one interference-type muffler section 75A, water can beseparated from air to a sufficient extent. Consequently, the throttlebody 42 can be supplied with air from which water has been separated toa sufficient extent (specifically, air that does not contain moisture).

Next, an example in which air intake noise produced along with airintake pulsations and shock waves while the engine 23 is being driven isreduced by the silencer 77 and the discharging/interference-type mufflermeans 75 shall be described on the basis of FIG. 24. To facilitateunderstanding of the example of reduction of air intake noise, in FIG.24, only the first intake passage section 73A (FIG. 9) is described.

As shown in FIG. 24 (a), air intake noise is produced along with airintake pulsations and shock waves while the engine 23 is being driven.The produced air intake noise is transmitted through the throttle body42 to the silencer lower half chamber 135 a of the silencer 77 shown inFIG. 24 (b), as shown by arrow W.

As shown in FIG. 24 (b), the silencer lower half chamber 135 acommunicates with the silencer upper half chamber 135 b through theopening 138. Consequently, air intake noise is reduced throughattenuation by the silencer 77 (the silencer chamber 135 (FIG. 4)).

The air intake noise attenuated by the silencer 77 is transmitted fromthe inlet port 136 of the silencer 77 to the side guide section 107 asshown by arrow X. The air intake noise transmitted to the side guidesection 107 is then transmitted to the one interference-type mufflersection 75A through the side guide section 107.

In specific terms, the air intake noise transmitted to the side guidesection 107 is transmitted from the side guide section 107 to the upperduct section 116 as shown by arrow Y, and then transmitted to the lowerduct section 117 as shown by arrow Z. The air intake noise transmittedto the upper duct section 116 is transmitted through the upper ductsection 116 to the guide port 112 as shown by the arrow Y.

Meanwhile, the air intake noise transmitted to the lower duct section117 is transmitted downward inside the lower duct section 117 to theascending step 128 as shown by the arrows Z. The flow of the air intakenoise transmitted to the ascending step 128 is redirected upward throughthe ascending step 128 and the center protruding section 126 as shown bythe arrows Z. At the interference position P1, the upwardly transmittedair intake noise (second air intake noise) interferes with the airintake noise (first air intake noise) that was directed from the sideguide section 107 to the upper duct section 116 as shown by the arrow Y.

At the interference position P1, the air intake noise (second air intakenoise) transmitted from the lower duct section 117 to the upper ductsection 116 as shown by the arrows Z undergoes an inversion of the phaseof the frequency with respect to the air intake noise (first air intakenoise) directed from the side guide section 107 to the upper ductsection 116 as shown by the arrow Y. Through interference of theinverted-phase second air intake noise with the first air intake noiseat the interference position P1 in this manner, the air intake noisetransmitted from the inlet port 136 of the silencer 77 can be reduced.

As described in FIG. 24, the silencer 77 and thedischarging/interference-type muffler means 75 (the oneinterference-type muffler section 75A) are included in the first intakepassage section 73A. This allows air intake noise to be reduced by boththe silencer 77 and the one interference-type muffler section 75A, whichenables air intake noise to be adequately reduced.

The outboard motor according to the present invention is not limited tothe embodiment described above, and various modifications andimprovements are possible. For example, the shapes and configurations ofthe outboard motor 10, the engine 23, the engine cover 24, the intakeopenings 26, the auxiliary machinery 41, the throttle body 42, the drivebelt 49, the belt cover 55, the intake passage 73, the pair of intakepassage sections 73A, 73B, the discharging/interference-type mufflermeans 75, the pair of interference-type muffler sections 75A, 75B, thesilencer 77, the guide bottom section 81, the air intake guide section87, the drain groove 91, the outer groove wall 97, the inner groove wall98, the pair of segmented duct sections 115, the guide ribs 122 and theseparation ribs 123, the silencer 77 and the drain port 129, the bodysection 132, the cover section, the silencer chamber 135, the silencerlower half chamber 135 b, the silencer upper half chamber 135 a, thesealing material 143, and the like are not limited to the exemplary onesshown herein; various modifications are possible.

INDUSTRIAL APPLICABILITY

The present invention is suited to application in an outboard motor inwhich an engine is disposed within an engine cover, and air drawn insidethe engine cover is allowed to be introduced into a throttle body.

REFERENCE SIGNS LIST

-   -   10: Outboard motor    -   23: Engine    -   24: Engine cover    -   24 b Both lateral sides of engine cover    -   24 c Rear wall of engine cover    -   26: Intake openings (openings)    -   35: Outside section of engine cover    -   41: Auxiliary Machinery    -   42: Throttle body    -   49: Drive belt    -   55: Belt cover    -   73: Intake passage    -   73A, 73B: Pair of intake passage sections    -   75: Discharging/interference-type muffler means        (interference-type muffler)    -   75A, 75B: Pair of interference-type muffler sections    -   77: Silencer    -   127 Bottom section    -   81: Guide bottom section    -   87 Air intake guide section    -   91: Drain groove    -   92: Rear drain groove section    -   93: Side drain groove sections    -   97: Outer groove wall    -   98: Inner groove wall    -   105: Vertical duct section (duct section)    -   115: Pair of segmented duct sections (duct sections)    -   122: Guide ribs    -   123: Separation ribs    -   129: Drain port    -   132: Body section    -   133: Cover section    -   135: Silencer chamber    -   135 a: Silencer lower half chamber    -   135 b Silencer upper half chamber    -   143: Sealing material

The invention claimed is:
 1. An outboard motor comprising: an engine; anengine cover covering the engine, the engine cover having a firstlateral side and a second lateral side opposite to the first lateralside; first and second intake openings provided in the first and secondlateral sides of the engine cover, respectively; a throttle body forintroducing air drawn inside the engine cover through the intakeopenings; and an intake passage that guides air from the first andsecond guide openings to the throttle body, wherein a muffler forreducing air intake noise is disposed partway along the intake passage,wherein the muffler is disposed vertically inside the engine cover, andthe muffler has an interior bisected in a vertical direction, wherein:the muffler with the interior thereof bisected in the vertical directioncomprises a first muffler section and a second muffler section, whereinthe intake passage includes a dual system having a first intake passagesection for guiding the air from the first intake opening provided inthe first lateral side of the engine cover to the throttle body, and asecond intake passage section for guiding the air from the second intakeopening provided in the second lateral side of the engine cover to thethrottle body, and wherein the first muffler section is disposed partwayalong the first intake passage section, and the second muffler sectionis disposed partway along the second intake passage section.
 2. Theoutboard motor of claim 1, wherein the muffler has a drain port formedin a bottom thereof that allows water, which has infiltrated inside themuffler, to be drained out of the muffler.
 3. The outboard motor ofclaim 1, wherein the intake passage is provided with a silencer forreducing air intake noise, the silencer being disposed downstream of themuffler and upstream of the throttle body.
 4. The outboard motor ofclaim 1, further comprising: a tubular air intake guide section disposedpartway along the intake passage and guiding in a vertical direction airthat has been drawn in from the intake openings; a vertical ductdisposed downstream of the tubular air intake guide section near a rearwall of the engine cover so as to be bisected in a vertical directionfor guiding laterally the air that has been guided vertically by thetubular air intake guide section; and first and second verticalseparation ribs disposed on the engine cover for impeding a flow of airthat has been guided laterally by the vertical duct.
 5. The outboardmotor of claim 4, wherein the vertical duct has an interior bisected inthe vertical direction and comprises a first duct section and a secondduct section, the intake passage includes a dual system having a firstintake passage section for guiding the air from the first intake openingprovided in the first lateral side of the engine cover to the throttlebody via the first duct section, and a second intake passage section forguiding the air from the second intake opening provided in the secondlateral side of the engine cover to the throttle body via the secondduct section, and the first vertical separation rib is disposed on theengine cover in a region thereof opposing the first duct section, andthe second vertical separation rib is disposed on the engine cover in aregion thereof opposing the second duct section.
 6. The outboard motorof claim 4, wherein the vertical duct has a drain port disposed in abottom section thereof.
 7. The outboard motor of claim 4, wherein thevertical duct has first and second guide ribs disposed such that airdirected into the vertical duct is guided by the first and second guideribs towards the first and second vertical separation ribs.
 8. Theoutboard motor of claim 1, further comprising: a silencer having asilencer chamber, the silencer being disposed upstream of the throttlebody in the intake passage; the silencer including: a body sectionforming a lower half section of the silencer chamber, the body sectionbeing disposed on a belt cover that covers from above a drive belt fordriving auxiliary machinery of the engine; and a cover section formingan upper half section of the silencer chamber, the cover section beingdisposed on the engine cover and being detachably disposed on the bodysection.
 9. The outboard motor of claim 8, wherein the silencer includesa sealing material between the body section and the cover section. 10.The outboard motor of claim 1, wherein the intake passage includes: atubular air intake guide section disposed to face in a verticaldirection in a region in which air drawn in through the first and secondintake openings flows in a substantially horizontal direction, thetubular air intake guide section being capable of separating water fromair drawn in through the first and second intake openings; a guidebottom section formed to extend between each of the first and secondintake openings and the tubular air intake guide section, the guidebottom section being sloped downward from the tubular air intake guidesection towards the first and second intake openings; and a drain groovedisposed in the guide bottom section, said drain groove guiding water,which has been separated by the tubular air intake guide section, fromthe tubular air intake guide section towards the first and second intakeopenings, the water guided into the first and second intake openings bythe drain groove draining out from the engine cover through the firstand second intake openings, wherein the drain groove has an outer groovewall disposed closer towards the intake openings, and an inner groovewall disposed further away from the intake openings, a height of theouter groove wall being greater than a height of the inner groove wall.11. The outboard motor of claim 10, wherein the drain groove is formedto have a downward pitch towards the intake openings from the intakeguide section.